"No one knows why we canceled the wedding, but I can tell you that all of the reasons that everyone is speculating and writing about are completely untrue," Foster told PEOPLE Monday, but she declined to reveal more about why the nuptials were called off.

Sources tell PEOPLE at issue were family matters (Usher's mother and former manager Jonetta Patton was against the wedding) and disagreements between the would-be-bride and groom over wedding details.

Foster, 37, who is now in Atlanta (as is Usher, 28) does address one rumor that spread on local radio stations and blogs – that following Saturday's canceled ceremony, she checked into a local hospital and went into pre-term labor.

Foster and Usher's nuptials were scheduled to take place this past Saturday at the Hamptons residence of Island Def Jam CEO L.A. Reid.

But hours before the scheduled ceremony, a source told PEOPLE that the 70 to 100 guests who were expected to attend were advised that it wasn't taking place as originally planned.

At the time, a publicist for the R&B singer, Patti Webster, said in a statement, "It was announced today that the wedding ceremony for Usher Raymond IV and Tameka Foster was canceled. No additional information will be given regarding the circumstances of the cancellation, but we hope the privacy of this matter will be respected."